Aspects of quarks in exotic matter

Sammanfattning: In this licentiate thesis, two different aspects of particle physics have been studied. The results are presented in four papers. In papers I and II, a model for a joint origin of gamma-ray bursts and dark matter is presented. The common denominator is the deconfined state of quarks, the Quark-Gluon Plasma (QGP). We propose that such quark objects surviving the quark-hadron transition in the early universe, constitute the dark matter and that mergers of these objects are the inner engine of gamma-ray bursts. We have computed stability criteria for macroscopic quark objects, as well as the merger frequency assuming a lognormal distribution in size. In paper III, the helicity amplitudes for rare-meson production invirtual gamma-gamma collisions are computed. We show that it is possible to apply a generalised version of the Brodsky-Lepage scheme for exclusive processes in QCD, when computing these amplitudes. In paper IV, we analyse consequences of the new supernova data, suggesting a non-zero vacuum energy density in the universe. We calculate the intrinsic luminosity correction for high-redshift objects such as gamma-ray bursts and quasars. Two different extensions of the Friedmann-Robertson-Walker universe are used; a non-zero cosmological constant and a time-dependent spatially inhomogeneous energy density component (so-called quintessence). The results show a correction of up to 30% for the conventionally computed luminosities.